Cold Model-Based Investigations to Study the Effects of Operational and Nonoperational Parameters on the Ruhrstahl–Heraeus Degassing Process

The circulation rate of steel is known to play a vital role in the superlative performance of the Ruhrstahl–Heraeus (RH) degasser. Numerous experiments were conducted on a physical model for the RH degassing process, which was established at IEHK, RWTH-Aachen University. The model was developed with a scale ratio of 1:3 to study the RH process. This study is conducted to show the effects of operational and nonoperational parameters on the circulation rate of liquid water in the model. The effects of lift gas flow rate, submerged depth of snorkels, water level in vessel, etc. on the circulation rate are studied. The mixing characteristics are studied with the help of current conductivity experiments for different lift gas flow rates and water levels in the vacuum vessel. Finally, the relationship between dimensionless numbers is derived with the help of the experimental data obtained from the cold model.     

Abnormal Failure Analysis of H13 Punches in Steel Squeeze Casting Process

In steel squeeze casting process, the working condition of a punch was very rigorous. The abnormal failure models of an H13 punch, such as plastic rubbed damnification, could not be avoided easily. Based on the analysis of the flow stress and the friction-shearing stress of an H13 punch in steel squeeze casting process, the following results were obtained： if the flow stress of an H13 punch was smaller than its friction-shearing stress, these abnormal failures could not be avoided; and if there were some protection measures that enable the flow stress to have a greater value than its friction-shearing one, the abnormal failures would not occur. In the production of 45^# steel valves and catenary system components, the flow stress of a lateral H13 punch without any protection measure was about 29 MPa and its friction-shearing stress was about 51 MPa, then, the abnormal failures occurred; however, when the protection measures of the punch enabled its working temperature to have a value below 682 ℃ its flow stress was greater than its friction-shearing stress, and the abnormal failures were avoided.     

Refractory–Slag–Metal–Inclusion Multiphase Reactions Modeling Using Computational Thermodynamics: Kinetic Model for Prediction of Inclusion Evolution in Molten Steel

The refractory–slag–metal–inclusion multiphase reaction model was developed by integrating the refractory–slag, slag–metal, and metal–inclusion elementary reactions in order to predict the evolution of inclusions during the secondary refining processes. The mass transfer coefficient in the metal and slag phase, and the mass transfer coefficient of MgO in the slag were employed in the present multiphase reactions modeling. The “Effective Equilibrium Reaction Zone (EERZ) Model” was basically employed. In this model, the reaction zone volume per unit step for metal and slag phase, which is dependent on the ‘effective reaction zone depth’ in each phase, should be defined. Thus, we evaluated the effective reaction zone depth from the mass transfer coefficient in metal and slag phase at 1873 K (1600 °C) for the desulfurization reaction which was measured in the present study. Because the dissolution rate of MgO from the refractory to slag phase is one of the key factors affecting the slag composition, the mass transfer coefficient of MgO in the ladle slag was also experimentally determined. The calculated results for the variation of the composition of slag and molten steel as a function of reaction time were in good agreement with the experimental results. The MgAl₂O₄ spinel inclusion was observed at the early to middle stage of the reaction, whereas the liquid oxide inclusion was mainly observed at the final stage of the refining reaction. The content of CaO sharply increased, and the SiO₂ content increased mildly with the increasing reaction time, while the content of Al₂O₃ in the inclusion drastically decreased. Even though there is slight difference between the calculated and measured results, the refractory–slag–metal multiphase reaction model constructed in the present study exhibited a good predictability of the inclusion evolution during ladle refining process.     

Process Simulation and Microstructure Analysis of Low Carbon SiMn Quenched and Partitioned Steel

The quenching and partitioning (Q&P) process was experimentally investigated on the thermomechanical simulator (Gleeble3800). The microstructure and fracture mechanism of the sheets were investigated by means of TEM. It was found that the microstructure of quenched and partitioned steel consists of fine lath martensite and thin interlath austenite films. The optimum quenching temperature of producing the maximum amount of retained austenite after final quenching at room temperature was predicted by Matlab software package. It was found that the calculations by Matlab software can provide guidance for experimental processing design reliably. The volume fraction of retained austenite at room temperature was approximately 8%, which was measured easily by the software VC60++ programming. The results verified that quenched and partitioned steel possesses a good combination of strength and plasticity due to its fine microstructure. This steel exhibited high ultimate tensile strength (exceeding 1 000 MPa) and good elongation of 25%. The results showed that the fracture mechanism of the sheets is typical tough fracture under the condition of tensile failure.     

Calculating Method for Influence of Material Flow on Energy Consumption in Steel Manufacturing Process

 From the viewpoint of systems energy conservation, the influences of material flow on its energy consumption in a steel manufacturing process is an important subject. The quantitative analysis of the relationship between material flow and the energy intensity is useful to save energy in steel industry. Based on the concept of standard material flow diagram, all possible situations of ferric material flow in steel manufacturing process are analyzed. The expressions of the influence of material flow deviated from standard material flow diagram on energy consumption are put forward.     

Analysis Microstructure of Weld Metal for HQ130+QJ63 High Strength Steel

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Theoretical Investigation on Deoxidation of Liquid Steel for Fe–Al–Si–O System

Deoxidation of liquid steel involves consumption of high energy materials like ferro alloys and generation of deoxidation products which could be entrapped into liquid steel as non-metallic inclusions. The present investigation is focused on deoxidation of liquid steel, considering mainly aluminium and silicon as deoxidizer. A simple and realistic mathematical model of deoxidation of liquid steel has been developed based on the thermodynamic principles and material balance approach for day to day industrial practice. One of the main aims of the theoretical study was to predict the amount of deoxidizers required for a given steel composition. A methodology has also been developed to predict the stability of different oxides expected to be present in liquid steel after deoxidation. Model predictions have been compared with the industrial data as well as results obtained from commercial thermodynamic software package FactSage 6.4, simulated under identical conditions. Model predictions are in reasonable agreement with the ferro alloy consumption in industrial steelmaking processes.     

Modeling of γ→α Transformation Temperature Ar3 for High-Nb Pipeline Steel During Cooling Process

 According to the research on the deformation resistance and the ferrite transformation behavior of X80 pipeline steel by using Gleeble-3500 thermal simulator, a mathematical model of the α-phase start transformation temperature for high-Nb pipeline steel was established, based on the transformation kinetics and thermodynamics. The influence of deformation and cooling rate as well as Nb content on the α-phase starting temperature was thoroughly investigated. The results given by the model were in good agreement with the experimental results, which showed that the model could predict the α-phase starting temperature for high-Nb pipeline steel during cooling process.     

Structure and Plastic Flow Heterogeneities of the 12Kh18N9T Steel–St3 Steel Bimetal during Tension

The plastic deformation of a three-layer bimetallic composite, namely, structural low-carbon St3sp steel clad by an austenitic corrosion-resistant 12Kh18N9T steel on both sides is studied. The laws of Chernov–Lüders band propagation during uniaxial tension and the load that corresponds to the yield strength are considered.     

Characteristic Analysis of Solidified Crust for Basic Tundish Flux With AlKilled Steel Casting

This present paper focused on the formation reasons of solidified crust when a basic tundish flux was used to cast the Al-killed steel. Crust samples were taken in an actual tundish, and analyzed by the methods of XRD, SEM and EDX. It was found that the main compositions of crystallization phases existing in tundish crust are Ca12Al4O33, Ca2SiO4 and a little spinel. Spinel and Ca2SiO4 distributed at grain boundaries of Ca12Al4O33, which increased the connection strength of crystallization phases by pinning the grain boundary, density or hardness of tundish crust will also significantly increased. When an initial composition of tundish flux was in spinel region of CaO-SiO2-Al2O3-10%MgO phase diagram, it was easier to form spinel in crust. Three approaches for spinel formation in crust were summarized. When flux is nearly saturated with magnesia, on the metal/flux interface, MgO in flux reduced by dissolved Al and formed the spinel. Inside molten steel and on the interface of steel/refractory, with a feasible Al content it is also easy to form spinel and spinel inclusions will float and captured by flux.     

Influence of process conditions during Ruhrstahl–Hereaeus refining process and effect of vacuum degassing on carbon removal to ultra-low levels

Abstract

The effect of the time taken to add the alloy and the gas injection mode are significant factors for fast decarburisation. Industrial experiments and thermodynamic calculations are adopted to show the transition of the main factors and reaction sites with time. The results indicate that adding steel scrap and alloy are not recommended in the first 7 min in order to keep good thermodynamic and dynamic conditions. The gas injection mode is more critical for reducing the chamber pressure to 67 Pa in 8.5 min and the gas volume should be less than 10 m³ in the first 4 min after the reaction begins. This method is effective in improving the decarburisation rate and decreasing the carbon content at the end of decarburisation. For 69% of the site tests the final carbon content was kept to about 10 ppm within 15 min.     

Time–Temperature–Precipitation Relations for Nitrides and Evaluation of Internal Oxidation Theory for Nitridation of Austenitic Stainless Steel

Metallurgical and Materials Transactions A - Internal nitridation kinetics were determined for a UNS N08810/800H alloy using a general model of the form $$x^{n}=kt$$ . Nitridation behavior was...     

Direct Calcification–Carbonation Method for Processing of Bayer Process Red Mud

The highly-alkaline red mud, which is the Bayer process residue generated from the alumina industry, is a severe environmental problem. In this study, a new calcification–carbonation process was proposed for red mud disposal. Red mud was processed by lime to convert the aqueous silicon phase into hydrogarnet, which was then decomposed by CO₂ to recover alumina. In the direct carbonation process, the NaOH-containing solution after calcification was directly carbonated without prior liquid–solid separation. The discrete and direct carbonation processes had alumina recovery rates of 34.9 and 35.5%, respectively, with 0.15 and 0.21 wt % Na₂O in the final red muds, respectively. The optimum NaOH concentration in the calcification liquor was 30 g/L. Under these conditions, alumina recovery was increased to 44.5% and the Na₂O concentration in the processed red mud was reduced to <1 wt %. The final red mud can be used as a construction material.     

Void Closure Behavior in Large Diameter Steel Rodduring H-V Rolling Process

In order to reveal the mechanism and condition of void closure in large diameter steel rod during horizontalvertical(H-V)groove rolling process,a three-dimensional thermomechanically coupled finite element model was established for 9-stand H-V groove rolling process aiming at a150mm steel rod production line.A spherical hole with diameter from 2to 10mm was preset into the center of continuous casting billet with a rectangle cross section of300mm×360mm in this model to simulate the void defect,and then finite element analyses were carried out to observe and quantify the void shape evolution in each pass on the three orthogonal coordinate plane sections.The results showed that the void was formed roughly in the reduction and extension directions,and crushed gradually from spherical shape to an approximate ellipsoid,micro-crack and finally to be closed.A quantitative analysis was carried out by using elliptic radii and closure ratio to describe this evolution process;it indicated that the longest axis of the ellipsoid coincided with the rolling line,and the second and third axes were alternatively horizontal and vertical on the exit cross section according to change of the reduction direction in H-V groove.The void closure behavior during HV rolling was more complicated than that of common horizontal rolling,and the influence of groove type and the extension coefficient on the void closure ratio was presented.Finally,apilot rolling experiment was performed on a 5-stand H-V experimental mill to verify the numerical simulation results,and the experimental results are in good agreement with the numerical simulation results.